1. Field of the Invention
This invention relates to a hand-held lighting device (e.g., a flashlight), wherein light is radiated from a mantle which is heated to incandescence by the combustion of a gaseous fuel such as isobutane.
More particularly, the invention relates to a fuel regulator particularly adapted for use in such a hand-held lighting device.
2. Description of the Prior Art
Valves for regulating the delivery pressure of a gaseous fuel are well known in the art.
In a hand-held device powered by liquefied gas, it is advantageous to employ a regulator which will deliver fully evaporated fuel at a specified pressure, regardless of the tank pressure, ambient opreating termperature or orientation of the device.
An ordinary needle valve is subject to the limitation that its delivery pressure varies in accordance with the fuel tank pressure, and thus a needle valve must be constantly readjusted in accordance with the ambient temperature. In a portable unit, which may be used in various orientations the problem is aggravated, since if inverted, a needle valve has a tendency to pass liquid fuel, resulting in a sputtering and erratic flame.
A number of pressure regulators are known in which a biased diaphragm is coupled to a variable valving mechanism. Varying the bias on the diaphragm controls the delivery pressure. Examples of this type of pressure regulators are to be found in Webster, U.S. Pat. Nos. 2,793,504 and 2,854,991; Baranowski, Jr., U.S. Pat. No. 3,699,998; Bowman et al, U.S. Pat. No. 3,736,093; Fleischacker et al, U.S. Pat. No. 3,812,877; and Curtis, U.S. Pat. No. 3,941,554.
Under normal operating conditions, the above-described type of pressure regulator achieves the object of supplying gaseous fuel at a prescribed delivery pressure, independent of the tank pressure. However, at low temperatures, when the fuel tank pressure falls below the delivery pressure, this type of regulator will deliver unvaporized fuel, if the device in which it is employed has been inverted.
Another known type of flow control element employs a porous plug interposed in the fuel stream, which retards the flow and induces a pressure drop, thereby evaporating the fuel.
For example, in Baumann et al, U.S. Pat. No. 3,388,962, there is shown a portable torch in which a sintered metal plug is provided upstream of a needle valve.
Similarly, Tissot-Dupont, U.S. Pat. No. 3,183,686, discloses a compressible porous element positioned in the fuel supply stream. The porosity of the element may be adjusted by varying the degree of compression to which it is subjected.
Like needle valves, the delivery pressure provided by such porous flow retarders varies with the ambient temperature. Additionally, porous flow retarders do not completely overcome the problem of liquid fuel passage at low temperatures.
Another approach to preventing the passage of liquid fuel is shown in Benzaria, U.S. Pat. No. 3,955,913, in which a miniature torch, designed to be held in the hand like a pencil, has a fuel feed tube which extends to the center of the fuel tank, which is then filled to slightly less than half full. Such an arrangement unduly limits the fuel capacity of a given device and is vulnerable to sudden movements.
Considering that passge of liquid fuel is most likely when the tank pressure is extremely low, due to low operating temperatures, it is desirable to provide a low pressure cutoff.
In Yost et al, U.S. Pat. No. 3,118,494 and Kinsella et al, U.S. Pat. No. 3,711,236, there are shown low pressure cutoff devices employing solenoids energized by thermocouples deployed adjacent pilot burners. These devices are relatively expensive, complicated, and best suited for use in gas-fired water heaters and the like.